7. Grain number density in the warm dust
In NGC 1068 , like in other AGN (see for instance NGC 7469), dust is present also in the NLR region (see Fig. 1). It has been shown in Sect. 5 that the infrared emission in the L & M bands over the region pc follows a power-law. In addition the temperature of the grains deduced from the [L-M] color has been found to remain roughly constant with radius. Thus, we can derive the radial profile of the warm grain number density in the NLR region, . Under optically thin conditions, probably applicable in the NLR, the brightness is directly proportional to the grain number density. Then the observed brightness power-law leads to =1.0, suggesting a concentrated grain distribution (a uniform grain density would correspond to =0). In NGC 7469, the warm dust component led to a figure for around 1.5 (Marco et al. 1998).
© European Southern Observatory (ESO) 2000
Online publication: December 17, 1999